Solenoid mechanisms generally include a coil and an armature that is free to move within the coil. The armature is normally spring loaded away from the energized position such that when a power pulse is applied to the coil, the armature is pulled into the energized position and in moving opens or closes the valve. In general, once the solenoid has moved to the end of its operating stroke, no further work is done by the armature.
The solenoid is often combined with a two-position valve, whereby the valve is pulled by the solenoid (when energized) and returned by a spring (when de-energized). The valve attached to the solenoid can be closed in one position and open in the second position, or it can be a changeover valve with two seats. In some applications, such as fuel injectors, it is desirable to measure and control the timing of the opening and closing positions of the solenoid operated valves.
Diesel fuel injectors need to have precise operating times. The valve determines the fuel injection timing. The valve also determines the fuel injection duration, which impacts the quantity of fuel injected into a cylinder of a diesel engine. The performance of the engine (balance between cylinders, power, fuel consumption, emissions) is thus affected.